1. Field of the Invention
The invention relates to copiers in general and more specifically to multiple nozzle ink jet copiers in which a plurality of ink jet nozzles are arranged in a plurality of linear arrays around the periphery of a rotating medium support drum and the scanned information from a document is prearranged in memory and later transferred to the linear arrays of nozzles at appropriate predetermined times to reproduce a copy of the scanned document on a medium supported on the drum.
2. Description of the Prior Art
Ink jet copiers in general generate digital information defining an image and applying the digital information either directly to an ink jet printer or printers or indirectly applying the same via a memory storage device which may or may not include rearrangement of the digital information. In those instances where multiple ink jet nozzles are employed, they may be arranged in a linear array parallel to the axis of a drum which supports the paper or other medium on which the image is to be formed. As the drum is rotated, the ink jet array is transported axially and the digital information is used to selectively control the ink jets to thus reproduce the image on the medium supported on the drum.
In those instances where multiple nozzle arrays are utilized, the images formed by each nozzle may follow interlaced spiral patterns on the medium. A perfect interlacing pattern is necessary to assure complete coverage and prevent double or multiple coverage of some areas on the medium. Several methods will provide such an interlace pattern of spirals.
The nozzle arrays may be fabricated such that the center to center spacing of the nozzles is made equal to the desired center to center spacing of the ink drops on the medium. This method provides automatic interlace, however, the required nozzle spacing is impractical if high printing resolution is required. Fabrication problems appear to render this solution unacceptable since the spacing, for any reasonable degree of resolution, is inadequate to accommodate the structural elements required to implement the required function.
Larger nozzle spacing in the array may be attained by angling the array with respect to the drum axis since the angling provides a closer axial drop spacing at the same time that it permits a larger nozzle spacing; however, this solution introduces a new problem. When the nozzle array is at an angle to the drum axis, the drops from the different nozzles in the array have different flight times due to the different distances to the drum surface. This produces varying degrees of drop misplacement depending on the number of nozzles and their spacing in the array. The problem of different flight times can be avoided by arranging the nozzles on a curved support plate which follows the drum contour so that all of the nozzles are equidistant from the drum surface. This solution is far from ideal since it requires a structure which is difficult to manufacture and align.
The nozzles and arrays may be staggered to provide additional space. However, this solution leads to additional problems in the areas of, driver uniformity, deflection when two or more rows are used, and guttering problems.
A more desirable solution would permit complete freedom on the center to center spacing of the nozzles which would allow a center to center nozzle spacing larger than the center to center spacing of the drops on the paper in the axial direction with negligible sacrifice of either printing speed or resolution. Such a solution would ease the fabrication of the nozzles and permit a much wider choice of existing nozzle technologies, such as glass drawn nozzle arrays or etched amorphous material arrays, all of which require substantial spacing. In addition, freedom of spacing minimizes problems in charge electrode packaging, guttering deflection systems and other problems related to electrical crosstalk are more readily solved.